Visual cryptography and voting technology

ABSTRACT

In some embodiments, techniques for voting and visual cryptography may include various enhancements.

RELATED APPLICATIONS

This application is a Continuation of Ser. No. 11/048,514 filed Jan. 31,2005, which claims priority to U.S. Provisional Patent Application No.60/540,723 filed Jan. 30, 2004, U.S. Provisional Patent Application No.60/554,668 filed Mar. 18, 2004 and U.S. Provisional Patent ApplicationNo. 60/580,270 filed Jun. 16, 2004, which are incorporated herein byreference for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to the area of security. Morespecifically, techniques for voting and visual cryptography aredisclosed.

BACKGROUND OF THE INVENTION

Voting is used for a wide variety of applications, including politicaloffices, corporate officers, and initiatives. Current voting technologydoes not provide adequate defenses against the manipulation of results,does not provide a voter-verifiable audit trail, suffers from poorquality in reconstructed ballot images, is susceptible to coercion, isvulnerable to malicious attacks and/or is cumbersome to use.

Accordingly, there is a need to improve the security and usability ofvoting.

Visual cryptography may be used to provide privacy. Existing visualcryptographic methods are difficult to align and construe, and providepoor grayscale rendering.

Accordingly, there is a need for improved visual cryptography.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a diagram of a system for voting, according to someembodiments.

FIG. 2 is a data flow diagram of a system for voting, according to someembodiments.

FIG. 3 is a data flow diagram of a system for generating a pseudorandomnumber and reconstruction escrow, according to some embodiments.

FIG. 4 is a data flow diagram of a system for reconstructing a numberfrom a reconstruction escrow, according to some embodiments.

FIG. 5 is a data flow diagram for an escrowing PRNG that provides anintegrated escrow for multiple PRNG contributors, according to someembodiments.

FIG. 6 is a data flow diagram for an escrowing PRNG that accumulatesrandomness from component escrowing PRNGs and nests their escrows,according to some embodiments.

FIG. 7 is a data flow diagram for an escrowing PRNG with more than oneindependent escrow, according to some embodiments.

FIG. 8 is a diagram of mix net permutations with and without challenges,according to some embodiments.

FIG. 9 is a diagram of the challenging of ⅔ of each round of a 6 roundmix net, according to some embodiments.

FIG. 10 is a flow diagram of a method for preparing and rendering a pairof lists for comparison, according to some embodiments.

FIG. 11 is a diagram of an aligned comparison of two lists using both aglyph and a color to represent a vote, according to some embodiments.

FIG. 12 is a flow diagram of a method for enhancing an overlay glyph,according to some embodiments.

FIG. 13 is a diagram showing samples of enhanced contrast overlayglyphs, according to some embodiments.

FIG. 14 is a flow diagram of a method for using enhanced glyphs,according to some embodiments.

FIG. 15 is a diagram illustrating combinations of perfectly alignedoverlaps of two overlay glyphs, according to some embodiments.

FIG. 16 is a diagram illustrating the result of combinations of alignedoverlays of glyphs, according to some embodiments.

FIG. 17 is a diagram illustrating the result of combinations of alignedoverlaps of glyphs, according to some embodiments.

FIG. 18 is a flow diagram of a method for using overlay glyphs to renderan array of data, according to some embodiments.

FIG. 19 is a flow diagram of a method for presenting overlays, accordingto some embodiments.

FIG. 20 is a flow diagram of a method for translating an overlay into anarray of data, according to some embodiments.

FIG. 21 is a flow diagram of a method for recovering a vote image,according to some embodiments.

FIG. 22 is a flow diagram of a method for incorporating alignment marksinto a rendering of data for overlay, according to some embodiments.

FIG. 23 is a flow diagram of a method for rendering and blurring anoverlay image, according to some embodiments.

FIG. 24 is an illustration of a set of overlay glyphs for use increating a gray level composite image, according to some embodiments.

FIG. 25 is a flow diagram of a method for constructing a set of overlayglyphs for presentation of gray levels, according to some embodiments.

FIG. 26 is a flow diagram of a method for encoding a gray level into twooverlay glyphs, according to some embodiments.

FIG. 27 is a flow diagram of a method for establishing authenticationcredentials, according to some embodiments.

FIG. 28 is a flow diagram of a method for creating a partiallyanonymized message, according to some embodiments.

FIG. 29 is a flow diagram of a method for processing a partiallyanonymized message, according to some embodiments.

FIG. 30 is a flow diagram of a method for distributing trusted software,according to some embodiments.

FIG. 31 is a flow diagram of a method for executing trusted software,according to some embodiments.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess, an apparatus, a system, a composition of matter, a computerreadable medium such as a computer readable storage medium or a computernetwork wherein program instructions are sent over optical or electroniccommunication links. In this specification, these implementations, orany other form that the invention may take, may be referred to astechniques. In general, the order of the steps of disclosed processesmay be altered within the scope of the invention.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

FIG. 1 is a diagram of a system for voting, according to someembodiments. In this example, a vote entry device 104 is connected to avoting booth processor 103. Examples of a vote entry device 104 includeany mechanism that accepts a selection from a voter for a set of on ormore ballot issues. Such a device may include a keyboard, touch screen,card reader, optical scanner, and pen tablet, as well as an electronicreader, including both optical and electronic memory readers, such asflash memory readers.

A voting booth processor 103 may include any system for translatingand/or encrypting a vote in preparation for processing and eventualtallying. An example of a voting booth processor 103 includes a generalpurpose computer configured to process votes, and a tamper resistantembedded processor and memory dedicated to such tasks.

In this example, a voting booth processor is connected to one or moredisplay devices 102. Examples of a display device include a printer,video display terminal, and LCD display terminal. In some embodiments,display devices 102 may be configured for performing overlay printing,for example printing on multiple sheets of paper and/or plastic fordisplay with a backlight to facilitate reading of composite imagery.

In this example, display device(s) 102 are connected to an overlay glyphenhancer 101. A glyph enhancer 2201 may modify glyphs or resultingraster scan data prior to rendering, for example to enhance a resultingcontrast ratio in an overlay display.

In this example, a voting booth processor 103, display devices 102, andoverlay glyph enhancer 2201 are connected to a network 112. Examples ofa network include an electronic communications network, such as a LAN orthe Internet, and a physical media communications network, such as apostal service a courier service. Such a connection may facilitatesoftware delivery to components, and/or facilitate transfer ofinformation about a vote

In this example, an audit records repository 111 is connected to one ormore networks 112. Audit records may include electronic and/or physicalrecords, such as paper records. For example, a voter verifiable audittrail may be stored in an audit records repository 111. In that example,a paper audit trail produced by display devices 102 may be delivered viaa network 112 to an audit repository 111. As a second example, auditableproof that tallying was done correctly, such as intermediate electronicresults in mix net processing performed by one or more trustees, may bestored in an audit records repository 111.

In this example, a vote aggregator 113 is connected to network(s) 112. Avote aggregator may include people and/or equipment, including data suchas decryption keys, that may process and tally votes, includingselection of valid and invalid votes. In some embodiments, a voteaggregator 113 may receive and authenticate absentee ballots inpreparation for, or as part of, aggregation. In some embodiments,physical votes provided by a courier may be aggregated. In someembodiments, electronic voting records may be tallied by an aggregator.In some embodiments, aggregation such as tallying may be performed onother aggregations, such as tallies previously performed. In someembodiments, aggregators may construct audit trails for inclusion in anaudit records repository 111 or a publications record repository 121,and/or extract information from a publication records repository 121 toassist in aggregation.

In this example, a publication record repository 121 is connected to thenetwork(s) 112. Examples of publication records include electronic andphysical records. In some embodiments, publication records may includeprivate or public records used to authenticate and tally votes. Forexample, records may include encryptions of votes produced by a votingbooth processor 103, intermediate aggregation results created and orused by a vote aggregator, and registration information or recordsconstructed by a voting registrar 122.

In this example, a voting registrar 122 is connected to the network(s)112. In some embodiments, a voting registrar 122 may validate identitycredentials and/or facilitate construction of authorized votingcredentials. Records of issued credentials may for example be recordedin publication or audit repositories 111 and 121, or in a separate datastore such as a database or filing cabinet. In some embodiments, avoting registrar 122 may assist in validation of voting credentials, forexample in support of a vote aggregator 113 authentication of acceptablevotes. In some embodiments, a voting registrar 122 may assist inabsentee ballot preparation, distribution, and authorization.

In this example, an absentee vote source 123 is connected to networks112. An example an absentee vote source is voter that completed anabsentee ballot for submission via a postal network. In someembodiments, an absentee vote source may be a personal computer andoptional printer that conveys the intent of a voter. Such intent may beconveyed via electronic submission or by production of a printed orprintable document. In some embodiments, trusted software may be used byan absentee vote source to reduce the potential for malicious softwareto corrupt a voter's intent. In some embodiments, trusted software maybe obtained from a trusted software distributor 124. In someembodiments, an absentee vote source may provide an absentee votethrough a physical medium, such as personal delivery or the US PostalService.

In this example, a trusted software distributor 124 is connected to anabsentee vote source 123, a voting booth processor 103, a voteaggregator 113, and network(s) 112. In some embodiments, a trustedsoftware distributor may provide software across a trusted channel,including for example hand delivery, in a format that is lesssusceptible to preexisting malicious software, such as a virus, worm, ormalicious configuration of a system. For example, a trusted softwaredistributor may include an operating system in a distribution.

FIG. 2 is a data flow diagram of a system for voting, according to someembodiments. In this example, a vote 207 is provided, for example in theform of a bit vector. In some embodiments, the vector may be ordered tomatch a list of one or more items that are being voted for/against, withone value, such as 1, indicating a vote for the item, and a differentvalue, such has 0, indicating a vote against the item. For example, thelist may consist of Gore and Bush, and a vote of (1,0) would be a votefor Gore, a vote of (0,1) would be a vote for Bush, and a vote of (0,0)would be an abstention. In some embodiments, the bit vector may be apixel array forming an image of a vote. For example, a bit mapcontaining 1's and 0's to represent dark and light pixels may be used todefine a raster image of a completed ballot. For example, a vote mayconsist of a 2-dimensional bit map for the rendering of the word “Gore,”or the rendering of the word “Bush,” or the rendering of a write-incandidate's name, as recorded by a scanner. In some embodiments, morethan one ballot issue may be included in a vote. For example, a vote mayinclude a voter's selection for a president (a first ballot issue), anda voter's selection for a dog catcher (a second ballot issue). Eachballot issue may include one or more ballot items. For example, apresidential election ballot issue may consist of a collection of ballotitems, such as nominated candidate names, initiatives and referenda.

In some embodiments, a vote may be combined via a bit-wise exclusive-OR(XOR) operation 212 with a pseudorandom bit vector WT generated by anescrowing pseudorandom number generator (PRNG) 211. An escrowing PRNGrefers herein to a PRNG that generates a pseudorandom value and data,referred to herein as a reconstruction escrow, that may subsequently beused to regenerate the pseudorandom value. One example of an escrowingPRNG is a “doll” as discussed in David Chaum, “Secret-Ballot Receipts:True Voter-Verifiable Elections,” IEEE Security & Privacy,January/February 2004, which is herein incorporated by reference for allpurposes. Another example of an escrowing PRNG is discussed inconjunction with FIG. 3. An XOR operation refers herein to an operationthat results in a value of 1 when source bits are different and a valueof 0 when source bits are identical. Another copy of the vote may becombined via XOR 213 with another pseudorandom bit-vector WB generatedby PRNG 214.

In some embodiments, the result of XORs 213, 212 may be assembled 220,221 along with the pseudorandom bit vectors WT, WB. In some embodiments,the assembly may include constructing vectors of 2-bit numbers, formedby concatenating component bits of the result of the XOR withcorresponding component bits of the pseudorandom vector. In someembodiments, the assembly 220 and 221 may be performed so that the mostsignificant bits (MSB) of the concatenation depend on one PRNG output,and the least significant bits (LSB) of the concatenation depend on theother PRNG. For example, the MSB in both assemblies may depend onescrowing PRNG 211 by using the value of WT in assembly 220 as the MSB,and using the value of XOR 212 in assembly 221 as the MSB. In such anexample, if an element in the vote bit-vector is 0, then the assembliesare identical for the corresponding elements in the assembled vectors220 and 221. Similarly, in such an example, if an element of the votebit-vector is 1, then the corresponding elements of the assembledvectors 220 and 221 are bitwise inverses of one and other.

The results of the assemblies 220 and 221 may be rendered in 241 and 243respectively. For example, rendering may include printing or displayingto a user. The method of rendering may be selected to facilitate thecomparison of the two outputs. For example, if a vote image wasprovided, then a set of glyphs appropriate for overlaying two printoutsmay be used, such as is discussed in conjunction with overlay glyphs inFIGS. 16 and 17. As a second example, if a vote vector corresponding toa list of items was provided, then XOR operations 212, 213 and assembly220, 221 may be omitted, and a data representation appropriate tofacilitating comparison of a list may be used, such as discussed inconjunction with FIG. 11. A user may compare the printed sheets producedby 241 and 243 to verify that the user's vote is accurately depicted inthe difference between the outputs. In some embodiments, a comparisonmay be performed using visual decryption, in which differences in theprinted sheets 241, 243 may be determined by overlaying the sheets sothat the differences form an image, such as an image of the vote. Insome embodiments, a comparison may be performed by aligning the printedsheets next to one another, and visually determining differences. Forexample, each sheet may contain a list of items, and portions of thoselists may be manually compared.

A user may select which of the two outputs created by 241 or 243 to useas a recorded encrypted vote. If a user selects rendering T produced in241, then in this example a pseudorandom seed RT and contents of sheet Tare digitally signed in 230 as SigRT, that signature along with RT isdisclosed in 240, and that disclosure along with the entire contents ofsheet T is published and/or recorded as a certified vote in 250. Anexample of publishing a sheet T is to make an image of T availablepublicly, for example on a web site. An example of recording a sheet Tis to retain a copy of T associated with a voting record, for example bystoring an electronic and/or physical copy of T. If the user selectssheet B as printed in 243, then in this example corresponding signing234, disclosure 244, and publication and/or recordation 252 areperformed. Disclosure in 240 or 244 may be achieved by printing thedata, for example as an additional printout on the associated sheet T orB provided in 241 and 243 respectively.

A reconstruction escrow for a pseudorandom number generator hereinrefers to encrypted information that may be used by trustees toreconstruct the pseudorandom output. Reconstruction escrows DT and DBproduced in 211 and 214 respectively may also be published or recordedin 232, in conjunction with a serial number Q provided by 203.

Renderings T and B produced by 1141 and 243 may also include informationderived from the serial number and reconstruction escrows DT and DB. Inthis example, cryptographic hashes of DT and DB are created by 231 and233 respectively, and then combined with the serial number in 215 toform a tuple. Examples of cryptographic hashes include MD5 and SHA1. Therendering of the tuple on the printed sheets may use a machine readablefont, such as a bar-code, or a human readable font, such as printedcharacters.

In some embodiments, seeds RT and RB used by the PRNGs 211 and 214 maybe produced by combining entropy sources, such as the tuples constructedin 210 and 215 respectively. A physical RNG (Random Number Generator)may use relatively unpredictable physical phenomenon as a source ofrandomness, for example events relating to radioactive decay. PhysicalRNGs 201 and 205 may contribute randomness PT and PB to 210 and 215respectively. A user may supply random values UT and UB in 202 and 204respectively. Examples of such a random value include a text stringentered by a user, and a user supplied value generated electronically orprovided on media, such as a paper, solid state, or magnetic media, andread by 202 and 204 respectively. A serial number 203, such as a machinegenerated number unique to a vote, may be combined with a secretcryptographic signing key by signing the serial number in 206 and 208,producing pseudorandom values ST and SB respectively. In one example,the same signing key may be used in both 206 and 208, and different datamay be signed, such as the tuple containing the serial number and “T” or“B” in the production of ST and SB respectively.

In some embodiments, the vote 207 may also be printed. A printed votemay be retained as a record of the vote. For example, a polling placemay retain and store such printed records. Such a printout may also beused as a means of tallying votes, as an alternative to, or astatistical or deterministic means of verifying, tallying via decryptionusing the reconstruction escrow. In some embodiments, a third layer witha distinctive color, such as a red layer, may be printed as a backgroundlayer to a visual decryption and contain the plaintext of a vote image,and that third layer may be preserved as a voter verifiable audit trail.An example of a visual decryption is an overlay of sheets T and B asproduced by 241 and 243 respectively.

In some embodiments, renderings T and B produced by 241 and 243 may alsoinclude machine readable redundancy data, such as an error correctingcode. For example, in a printed rendering including a vote imageencrypted using visual cryptography, a machine readable error correctingcode may also be printed. Such an error correcting code may be used tofacilitate scanning of a printed (encrypted) ballot, for example as partof a ballot validation. Examples of error correcting codes includeparity codes, Hamming codes, and Reed-Solomon codes.

FIG. 3 is a data flow diagram of a system for generating a pseudorandomnumber and reconstruction escrow, according to some embodiments. In thisexample, a high entropy seed R is provided in 300 and a resulting k bitpseudorandom output W is generated in 398, along with a reconstructionescrow D in 399.

In this example, there are L stages of contribution to the generatedoutputs. For example, L may be 8. Each stage combines some informationfrom a prior stage (if any) with data generated in that stage, andproduces data for the next stage (or for the final output W and D). Forexample, in the third stage, the secret seed R from 300 iscryptographically hashed in 331 with a value 330 that is unique to thisthird stage. In this example, a value of 3 is used in the third stageand supplied by 330. Examples of a cryptographic hash include MD5 andSHA-1. The result of that third stage hash herein referred to as E3, thestage's seed, may used in the third stage's PRNG 332. One example of astage's PRNG is an RC4 encryption of a stream of zeros, where the keyfor the encryption is the seed for the PRNG. Each stage's PRNG providesk bits, which are accumulated via XOR operations into the k bit output Win 399.

Each stage also encrypts via a public key the accumulated escrow fromthe previous stage (if any), along with the stage's internal values, toconstruct an escrow for use in the next stage (or as the finalreconstruction escrow D). For example, in the third stage, the secondstage escrow D2 produced in 329 is encrypted in 339. The encryption inthis third stage uses a public key referred to herein as Pub3. Theencrypted data may also include E3 (the stage's seed) and G3 from 331and 336 respectively. The third stage value G3 may be computed in 336 byhashing a value provided in 330 that is unique to this third stage,along with a constant C provided by 335. In some embodiments, the secondhash, such as G3 in the third stage, may not be included in theencrypted escrow, such as 339 in the third stage.

In some embodiments, an escrow from an external escrowing PRNG may beprovided in 301. In some embodiments, no escrow chaining input isprovided, and the first stage of an escrowing PRNG encrypts internalvalues for the first stage to provide an escrow to the next stage.

FIG. 4 is a data flow diagram of a system for reconstructing a numberfrom a reconstruction escrow, according to some embodiments. In thisexample, a reconstruction escrow D provided in 400 is decrypted toreconstruct a value W in 499. In some embodiments, W may be apseudorandom value that was originally generated in conjunction with theescrow, such as discussed in conjunction with FIG. 3.

A reconstruction may consist of L stages, corresponding to the number ofstages in the escrow generation. For example, L may be 8. In each stageof the reconstruction an escrow from the previous stage (or the originalescrow input) is decrypted, providing data for that stage, andoptionally providing an escrow to be processed in the next stage. Forexample, in the third from the last stage of FIG. 4, escrow D3 isdecrypted in 430 using private key Priv3. In this example, Priv3 is thecorresponding private key for the public key Pub3 as discussed inconjunction with 339 of FIG. 3. The decryption may provide an escrow D2for use in the second to the last stage, and may also provide E3 and G3as were discussed in conjunction with FIG. 3. The value G3, if itexists, may be discarded in this example. The value E3, the stage'sseed, may be used by a PRNG 431 to produce a k bit contribution (in thisexample via xor) to the complete k bit number W. If an escrow chaininginput such as 301 of FIG. 3 was provided during the construction of theescrow D, then that escrow chaining value is recovered in 498 in thisexample.

FIG. 5 is a data flow diagram for an escrowing PRNG that provides anintegrated escrow for multiple PRNG contributors, according to someembodiments. In this example, a high entropy secret seed R 500 is usedto generate a pseudorandom KM×N bit result, along with a reconstructionescrow D 598. An optional escrow chaining input 501 is also supported,as was discussed in conjunction with FIG. 3.

In a voting application such as discussed in conjunction with FIG. 2,when a vote consists of an image with K distinct ballot issues, then anindividual M×N bit array may be used to encrypt each of the ballotissues. In a voting application such as discussed in conjunction withFIG. 2, when a vote consists of a list of M or fewer discrete optionsfor each of the K ballot issues, then an M×1 generated list of bits maybe used to encrypt a portion of the vote corresponding to each ballotissue.

Internal to this example PRNG are K separate escrowing PRNGs, each ofwhich may generate an M×N bit pseudorandom array. Each component PRNG isseeded with a combination of a value dependent on the component number,and the secret seed R 500. For example, 519 is the K^(th) PRNG, and itmay use a secret seed consisting of the concatenation of R 500 with thenumber K. It produces an M×N bit pseudorandom number denoted WK, and anescrow denoted KD. The first PRNG 510 in this example may also accept anexternal optional escrow chaining input 501 (if any), and incorporate itinto its resulting escrow output denoted 1D.

The K component M×N bit random numbers arrays, denoted W1 . . . WK, maybe appended together in 596 to create a KM×N bit array. The resultingcombined array may serve as the overall PRNG output W in 599.

The K component escrows, denoted 1D . . . KD, may be combined in 597 tocreate the overall escrow. For example, they may be listed as a Kelement tuple, and serve as the overall reconstruction escrow output598.

In some embodiments, internal encryption keys may be different forescrow encryption contained in the K component PRNGs. Examples ofencryption keys used in escrowing PRNGs include those discussed inconjunction with 339 of FIG. 3. In some embodiments, various trusteesmay possess corresponding private keys. In such examples, differenttrustees may be required to decrypt the escrows that are generated invarious component PRNGs. In some embodiments, this separation allows anencrypted vote image to be broken into separate ballot issues beforecomplete decipherment. The separate encrypted ballot issues may bedeciphered in separate groups. In such an example, a vote on one ballotissue, decoded by one set of trustees, may not be immediately correlatedwith a vote cast by the same voter for a different ballot issue.

FIG. 6 is a data flow diagram for an escrowing PRNG that accumulatesrandomness from component escrowing PRNGs and nests their escrows,according to some embodiments. In this example, N bits of randomnessfrom escrowing PRNGs 630 and 620 are combined via an XOR operation toprovide a final N bit output W 699. The escrow output from the escrowingPRNG 620 may be used as an escrow chaining input into PRNG 630, which inturn may produce a complete reconstruction escrow D 698.

In some embodiments, an escrowing PRNG 620 or 630 may be constructed asdiscussed in conjunction with FIG. 5 or 6.

The high entropy secret seed R 600 may provide entropy to one or bothcomponent PRNGs. The escrowing PRNGs 630 and 620 may use R inconjunction with another value, such as a constant, to create a uniqueentropy input. In this example, the tuple containing the word “Post” andthe entropy R is provided to the escrowing PRNG 630, and the tuplecontaining the word “Pre” and the entropy R is provided to the escrowingPRNG 620.

FIG. 7 is a data flow diagram for an escrowing PRNG with more than oneindependent escrow, according to some embodiments. In this example, twoescrows Da and Db are created in 799 and 798 respectively. Each escrowmay optionally have an escrow chaining input, such as 708 and 709.

In this example, the PRNG has L stages, and an individual stage may hashtogether a combination of an external high entropy secret seed R inputin 700, and a value specific to the stage. For example, in the thirdstage, the constant 3 shown as 730 is hashed with R in 731 to constructa stage seed E3. One copy of that stage seed E3 is used as an input to asimple PRNG 732. An example of a simple PRNG is an RC4 cipher streamgenerator, using its input as a key, and configured to providecontributions via XOR to the final pseudorandom output W in 795.

An escrow chain may contain nested encryptions of all stage seeds. Forexample, in the third stage, the escrow chain that began with “optionalescrow chain a” in 708 may encrypt in 738 using public key a3 acombination of the stage seed E3 from hash 731, along with encryptedresults from the second stage provided by 728.

In some embodiments, additional stage secret information may beencrypted in each stage, such as the stage secret G3 data produced by336 and discussed in conjunction with FIG. 3. In some embodiments, suchadditional data in a stage may be distinct for each escrow chaincreated, for example by using different constants such as 335 of FIG. 3for each escrow construction, creating different contributions to theconstruction of Da vs. Db.

In some embodiments, one or more additional escrows may use a differentnesting order, and/or encryption keys associated with differenttrustees, for encryption. In this example, a second escrow has anencryption nesting ordering for the escrow Db in 799 that is the exactopposite of the ordering for construction of Da in 798. For example, thethird from the last encryption in the construction of Db may use publickey b3 to encrypt E3 (and any nested encryptions) with the resultscontributed to 729 for encryption in the second to the last encryptionin the formation of Db. In some embodiments, the nesting order may be apermutation of the ordering of another escrow's nesting order.

In some embodiments, private keys associated with different escrows maybe known to various trustees. In some applications, these distincttrustees may be able to provide either backup decoding services fortrustees in other chains, or may provide auditing capabilities to verifydecoding done by other trustees. For example, in a voting applicationsuch as was discussed in conjunction with FIG. 2, additional escrows maybe combined, for example by concatenation or placement into a tuple, tocreate a redundant escrow. In such a system, either escrow may be usedto decipher a vote by extracting an individual escrow from a redundantescrow.

FIG. 8 is a diagram of mix net permutations with and without challenges,according to some embodiments. A mix net refers herein to a system thataccepts a list of encrypted inputs, and produces a corresponding list ofdecrypted or differently encrypted outputs, where only the entity thatperforms the processing is privy to exactly which input items areassociated with which output items. In this example, 801 depicts theprocessing and mixing of list of 8 elements, identified with the letters“A” through “H”, producing a list of 8 elements, labeled “A-H” toindicate the uncertainty to an external observer as to whether eachelement was associated with any one of the 8 specific input elements. Inthat example, after a complete input and output list is defined, anexternal observer may “challenge” the correctness of some members of thelist (either input or output, or both). A challenge consists ofidentifying some subset of the list elements, in this case 50%, or 4elements, and asking that the trustee prove that these elements werecorrectly translated. Such a proof may include, for each challengedelement, identification of the corresponding elements in the input andoutput lists, and proving their correlation. For example, a proof ofcorrelation may consist of revealing a secret which can be used toverify the correlation. An example of a secret that may be used toverify a correlation is one or more values that, when combined with anoutput and encrypted using a predetermined cryptographic key, yields acorresponding input.

The depiction 802 illustrates the result of such a partial challenge of4 elements. For illustrative simplicity, the challenged inputs have beenlabeled “E” through “H,” and the unchallenged inputs have been labeled“A” through “D.” The illustrations shows that 4 of the outputs, labeled“E” through “H” are known to correlate to the identically named inputs,and 4 of the outputs labeled “A-D” are known only to correlate to the 4unchallenged outputs.

In some embodiments, several mix nets with intermediate challenges maybe sequentially composed to construct a mix net for which there is noexternally visible correlation between the input list and output list.An example of this is the composition of 4 mix nets in 803, in whicheach intermediate mix net has 50% of its elements (in this example, 4per round) challenged. To achieve this result, the challenges in thefirst round may be randomly chosen (and/or chosen by another trustedparticipant) and produce an intermediate list represented exactly as wasthe output list of 802. For the second round, challenges may be made forthe elements that were not challenged the first round, and theintermediate list that results has half of its elements shown as “A-D”correlated to some unknown input between “A” and “D,” while the otherhalf are labeled “E-H” and correlated to some unknown input between “E”and “H.” In the third round, half of the challenges may be taken fromlist elements challenged in the first round, labeled “A-D,” and half maybe taken from list elements challenged in the second round, labeled“E-H.” The selection may be random, and/or done by another trustedparticipant. As a result, the unchallenged outputs from the third roundare equally likely to correlate to “A-D” as to “E-H,” and hence arelabeled “A-H.” The challenged elements output in the third round retaintheir uncertainty, and are labeled either “A-D” or “E-H” respectively.In the fourth round, challenges may be made to elements that were notchallenged in the third round. As a result, the unchallenged elements ofthe fourth round are equally likely to be correlated to “A-D” as to“E-H,” and hence all outputs from the fourth round are labeled “A-H.”

For any integer P greater than 2, the above approach may be used when achallenge rate of P−1 out of P elements per round is employed (P was 2in the above example), and a composition of at least 2×P rounds of mixnets are utilized. In various embodiments, P may be equal to 3, 4, 5, 6,7, 8, 9 or 10. If the number of elements in the list to be processed isnot a multiple of P×P, then additional list elements may be added to thelist before processing, for example inconsequential elements. Examplesof inconsequential elements in a mix net processing ballots includeballots with only abstentions, and ballots that are specially encoded toindicate that they are not actual votes. With a multiple of P×P listelements, and at least 2×P rounds of mix nets to challenge, thechallenges may be made as follows. In each of the first P rounds, a setof 1/P of the list is unchallenged in that round. The selection may bemade by establishing challenges for the first round, then second round,etc. The challenges may be selected in each round such that if anelement is unchallenged in a round, then that element is challenged inall of the other rounds up to round P. Subject to the above constraint,selections may be made, randomly, pseudorandomly, or by a trusted party.

Starting with round P+1, and continuing to round 2×P, a differentselection constraint may be used. In each successive round, theunchallenged set of list items may consist of 1/P of each of the listitems challenged in each of the first P rounds. For example, 1/P of theitems unchallenged in round 1, plus 1/P of the items unchallenged inround 2, . . . plus 1/P of the items unchallenged in round P, may beselected to be unchallenged in successive rounds. An additionalconstraint on the selection may be that any item that is unchallenged inthese later rounds (P+1 . . . 2×P) is challenged in all subsequentrounds up to round 2×P.

FIG. 9 is a diagram of the challenging of ⅔ of each round of a 6 roundmix net, according to some embodiments. In this example, the approachdescribed in conjunction with FIG. 8 is used in which P is 3, the numberof rounds 2×P==6, and the challenge rate is (P−1)/P==⅔ per round. Forillustrative reasons, a total of 9 list elements is shown in thisexample, which is a multiple of P×P (3×3==9). As was depicted in FIG. 9,unchallenged items in a mix net are represented by a circle takinginputs on the left, and producing outputs on the right. The far leftcolumn has input elements labeled “A” through “I”, and the final outputhas list elements labeled “A-I” to indicate that the correlation withthe original list is unknown.

FIG. 10 is a flow diagram of a method for preparing and rendering a pairof lists for comparison, according to some embodiments. In this example,a pair of lists is received (1001). A “list” refers herein to an orderedseries of items. For example, the following is a list of 16 items, eachof which is an integer in the range from 0 to 1: [0 0 0 1 1 1 0 0 1 0 10 1 1 0 1]. As a second example, the following is a list of 8 items,each of which is an integer in the range from 0 to 3: [0 1 3 0 2 2 3 1].A third example is a list of 8 items, each of which is a tupleconsisting of two binary digits: [(0 0) (0 1) (1 1) (0 0) (1 0) (1 0)(1 1) (0 1)].

An encoding and layout may be selected for the lists (1002). In someembodiments, lists of items may be laid out so that correspondingelements are adjacent to each other. For example, if lists of pairs ofbinary digits are laid out horizontally, then the following is anexample of an element-by-element aligned list:

(0 0) (0 1) (1 1) (0 0) (1 0) (1 0) (1 1) (0 1) (0 0) (0 1) (1 1) (0 0)(1 0) (0 1) (1 1) (0 1)

The following is an example of the same pair of lists, with thedifferent element again in the sixth position, with a vertical layout.

(0 0) (0 0) (0 1) (0 1) (1 1) (1 1) (0 0) (0 0) (1 0) (1 0) (1 0) (0 1)(1 1) (1 1) (0 1) (0 1)

In some embodiments, alignment may be horizontal. In some embodiments,alignment may be vertical. We refer herein to a visual comparison oflists using adjacent element placement as an “aligned comparison.”

To illustrate colors in this document, which may be printed in black andwhite, uniform color regions will be surrounded in square brackets “[”and “]”. The first or last character in each enclosed region will beused to denote the constant color used for the foreground characters inthat region, such as “r” for red, “b” for blue, “g” for green, and “n”for normal black. For example, text of the form “[b 123] [456 g]” willbe used to represent the text “123 456” with the first three characterprinted in blue, and the last three characters printed in green.

In some embodiments, the foreground and/or background color for elementsin a list may be selected (1002) based on each element to facilitate analigned comparison. For example, the following color map may be used todisplay elements that are associated with pairs of binary digits:

(0 0) displays as Red on a white background [(0 0) r]

(0 1) displays as Blue on a white background [(0 1) b]

(1 0) displays as Green on a white background [(1 0) g]

(1 1) displays as Normal (e.g. black) on a white background [(1 1) n]

In some embodiments, a character, word or glyph representing the colorpattern may optionally be appended (or prepended) to the colorizedregion (or comparable region) as part of the encoding of the lists.

As an example, the above foreground coloring of binary pairs may be usedin the initial example of an aligned comparison of two lists, producingthe following:

[(0 0) r] [r (0 0)] [(0 1) b] [b (0 1)] [(1 1) n] [n (1 1)] [(0 0) r] [r(0 0)] [(1 0) g] [g (1 0)] [(1 0) g] [b (0 1)] [(1 1) n] [n (1 1)][(0 1) b] [b (0 1)]

In the above colored list example, the sixth element is identifiable bycolor as the point where the lists differ, and the fact that the otherelements are identical may be visually verified by color as well.

In some embodiments, a more compact and visually discernable glyph may,as part of the encoding, replace a set of glyphs in a list rendered ordisplayed for an aligned comparison. For example, if the number ofdistinct elements subject to comparison, formed by combinations ofglyphs, is small, then a small set of glyphs can be used in place of, orin addition to, each of the comparable elements. For example if elementsto compare in a list are pairs of binary digits, then there are no morethan four possible pairs, and a unique glyph may be used in place ofeach comparison element. In such an example, the display or renderingcould be:

(0 0) displays as ↑

(0 1) displays as ←

(1 0) displays as →

(1 1) displays as ↓

For example, representing the previous example of an aligned list of 8pairs of binary digits using only the above glyph, the aligned listcomparison would look like:

↑ ↑ ← ← ↓ ↓ ↑ ↑ → → → ← ↓ ↓ ← ←

In the above list, the sixth element is discernable as the point wherethe lists differ, and the fact that the other elements are identical isalso verifiable.

In some embodiments, both a more compact glyph and a color mapping maybe used as part of the encoding. For example, the original list could bepresented for aligned comparison with pairs of binary digits in thefollowing representation:

(0 0) displays as [↑r]

(0 1) displays as [←b]

(1 0) displays as [→g]

(1 1) displays as [↓n]

In some embodiments, as part of the encoding, a replacement glyphmapping may be chosen that evidences a relationship between differingelements in an aligned comparison. For example, in addition todistinguishing the differing element(s) in the original alignedcomparison of pairs of binary digits, it may be useful to verify thatthe differences, if any, all satisfy some relationship, such as theinverting of binary digits. In such an example, it is necessary toverify for differing elements that pair (0 0) is only adjacent to pair(1 1), and pair (1 0) is only adjacent to pair (0 1). The above compactglyph example using horizontal and vertical arrows is an example of aglyph mapping that facilitates such comparison, as both (1 1) and (0 0)use vertical arrows, which match when pointing in the same direction,but demonstrate bit inversion when pointing in opposite directions.Similarly, the horizontal arrows represent the pairs (1 0) and (0 1),and indicate a perfect match when pointing in identical directions, andrepresent bit inversion when pointing in opposite directions. Anydistinguishable glyphs that share some common readily apparentattribute, such as orientation (as demonstrated with the arrow glyphs),fill pattern, background or foreground color, shape or placement, may beused to verify a level of commonality in the corresponding differingelements.

In some embodiments, encoding may vary from list to list. In someembodiments, one glyph (or color) map may be used for rendering ordisplaying one list for an aligned comparison, while a different map maybe used to render or display a second list. For example, the use of thearrow head glyphs could be modified so that the right hand list usedglyph maps with arrow heads that have opposing direction (on a perelement basis) to the glyph maps used for the left hand list. Theresulting aligned comparison of the initial example of 8 pairs of binarydigits would then appear in this example as:

↑ ↓ ← → ↓ ↑ ↑ ↓ → ← → → ↓ ↑ ← →

In this example, if all differences between compared list items areknown to satisfy an aforementioned relationship (for example arelationship wherein pairs of binary digits are inverted) then such arepresentation may highlight the differing sixth item. All “differingbinary digit” items in that example appear with identical glyphs (orcolors) in corresponding positions in this example.

In some embodiments, the list encoding and layout selected may be usedto represent portions of a voting ballot that represents a vote as oneor more similarities and/or differences between elements of two lists.For example, as discussed in conjunction with FIG. 2, when a votesupplied in 207 is an ordered list of 0's and 1s, corresponding to voteselections for an ordered list of candidates, then 220 and 221 assemblelists of pairs of bits for comparison. For example, in an election witheight candidates, a blank ballot, with no votes cast, based on a oneseeded PRNG encryption, might be represented by the following pairs ofbinary digits:

1 2 3 4 5 6 7 8 0 0 0 1 1 1 0 0 1 0 1 1 1 1 0 1 0 0 0 1 1 1 0 0 1 0 1 11 1 0 1

With the same seeded PRNG encryption, if a single vote was registered,such as for the sixth candidate, the two lists to differ as shown:

1 2 3 4 5 6 7 8 0 0 0 1 1 1 0 0 1 0 1 0 1 1 0 1 0 0 0 1 1 1 0 0 1 0 0 11 1 0 1

A selected layout may include additional formatting and data. In someembodiments, the candidate names or descriptive text may be rendered ordisplayed on a ballot along with the actual vote, as encrypted intodifferences between two lists. For example, candidates corresponding tothe eight candidates above may be named:

1. Goofy

2. Minnie

3. Mickey

4. Donald

5. Pluto

6. Huey

7. Dewey

8. Louie

The above ballot with a vote cast for Huey, the sixth element in thelist, might be encoded as:

Goofy (0 0) (0 0) Goofy Minnie (0 1) (0 1) Minnie Mickey (1 1) (1 1)Mickey Donald (0 0) (0 0) Donald Pluto (1 0) (1 0) Pluto Huey (1 0)(0 1) Huey Dewey (1 1) (1 1) Dewey Louie (0 1) (0 1) Louie

The two columns are examples of what may be rendered in 241 and 243respectively, as discussed in conjunction with FIG. 2, when the vote 207is a list of 1's and 0's for each of the 8 candidates.

A selected layout and encoding may include additional information, suchas aggregate information about the list, or the meaning of the list, oradditional reference or authentication information. In some embodiments,some or all information presented on the ballot list may be included inthe hash or resulting signature for a printout. Examples of signatureson printed sheets include 230 and 234, as discussed in conjunction withFIG. 2. For example, the candidate names, as presented in the abovelist, may be included on the above sheets and signed as appropriate, ora hash of the name list may be included on the sheets and signed asappropriate, or the name list or its hash may be implicitly included onthe sheets and signed as appropriate. As a second example, thedefinition of any glyph or color mapping may be implicitly included orprinted and explicitly included in signatures created for the abovesheets.

A selected encoding may include coloration that may be applied to someor all of a list item, and may be based upon data in that item. As anexample the following color map may be used to render the completed (andencrypted) ballot described above:

(0 0) displays as Red on a white background [(0 0) r]

(0 1) displays as Blue on a white background [(0 1) b]

(1 0) displays as Green on a white background [(1 0) g]

(1 1) displays as Normal black on a white background [(1 1) n]

If the above coloring is applied to the entire line, the above ballot isencoded in this example as:

[Goofy (0 0) r] [r (0 0) Goofy] [Minnie (0 1) b] [b (0 1) Minnie][Mickey (1 1) n] [n (1 1) Mickey] [Donald (0 0) r] [r (0 0) Donald][Pluto (1 0) g] [g (1 0) Pluto] [Huey (1 0) g] [b (0 1) Huey] [Dewey(1 1) n] [n (1 1) Dewey] [Louie (0 1) b] [b (0 1) Louie]

The above list highlights the fact that the vote is for the Huey byusing different colors on the left vs. the right column for the castvote. The explicit presence of the binary digits is optional in theabove presentation, and it is implied by the color. For example, thelists could be encoded as:

[Goofy r] [r Goofy] [Minnie b] [b Minnie] [Mickey n] [n Mickey] [Donaldr] [r Donald] [Pluto g] [g Pluto] [Huey g] [b Huey] [Dewey n] [n Dewey][Louie b] [b Louie]

In some embodiments, different color maps may be chosen for each sidesuch that an encoded difference will show as the same color, while nodifference will show as a different color. As an example, the aboveballot may be encoded using the following color map only for the righthand column, while using the previous example color map again for theleft hand column:

(0 0) displays in right column as Normal black on a white background [(00) n]

(0 1) displays in right column as Green on a white background [(0 1) g]

(1 0) displays in right column as Blue on a white background [(1 0) b]

(1 1) displays in right column as Red black on a white background [(1 1)n]

The completed ballot would then be encoded in this example as:

[Goofy (0 0) r] [n (0 0) Goofy] [Minnie (0 1) b] [g (0 1) Minnie][Mickey (1 1) n] [r (1 1) Mickey] [Donald (0 0) r] [n (0 0) Donald][Pluto (1 0) g] [b (1 0) Pluto] [Huey (1 0) g] [g (0 1) Huey] [Dewey(1 1) n] [r (1 1) Dewey] [Louie (0 1) b] [g (0 1) Louie]

In the above example with the above set of left and right colormappings, the vote is indicated by a consistent color in the adjacentcolumns, as seen in the sixth entry, where green is uniformly used. Thepresence in the presentation of the actual binary digit pair or relatedglyph or representation is optional in the above example.

In the following example, the completed ballot from the previousexamples is encoded using the compact arrow head glyph to represent thebinary digit pairs, with the same glyph map used in both the left andright column:

Goofy ↑ ↑ Goofy Minnie ← ← Minnie Mickey ↓ ↓ Mickey Donald ↑ ↑ DonaldPluto → → Pluto Huey → ← Huey Dewey ↓ ↓ Dewey Louie ← ← Louie

In the above example, the differing arrows on the line with Hueyidentify the vote expressed in this ballot.

Lists may be rendered for comparison (1003). For example, they may beprinted. Although the above examples were printed with elements next tocorresponding elements in the second list, the lists may be printedseparately and manually or automatically aligned for a visualcomparison.

FIG. 11 is diagram of an aligned comparison of two lists using both aglyph and a color to represent a vote, according to some embodiments. Inthis example, a color and a glyph are both used to represent each binarydigit pair (shown in the previous completed ballot examples), and theleft and right maps (for both glyphs and colors) were chosen asdescribed earlier so that the vote in the ballot is apparent frommatching glyphs, and matching colors. As noted earlier, the squarebrackets “[ ]” in the Figure are present only for illustrative purposesto designate the extent of color, and the color selection is provided bythe letter “b,” “r,” “g” and “n” just inside such brackets. Printedblocks 1101 and 1102 are examples of portions of the printout that maybe provided in 241 and 243 respectively, as discussed in conjunctionwith FIG. 2.

In this example, a vote for “Huey” is presented. The sixth entry in theleft list 1101 with the candidate name “Huey” 1103 is colored green, andis associated with a right pointing arrow glyph. The sixth entry in theright hand list 1102 with the candidate name “Huey” 1104 also is coloredgreen, and is associated with a right pointing arrow glyph. All othercandidates have non-matching colors on the two lists, and also havenon-matching directed arrow glyphs on the two lists.

In some embodiments, when the number of listed options to cast a votefor is small, for example less than 3 listed options total, one or moreadditional options may be listed to indicate alternatives, such as“abstain.” For example, if a vote is for a referendum where the twopossible votes are “vote for Yes” and “vote for No,” a third listedentry of “abstain” may be provided.

FIG. 12 is a flow diagram of a method for enhancing an overlay glyph,according to some embodiments. In this example, an overlay glyph isreceived (1201). Examples of overlay glyphs include glyphs that may beprinted, with various glyphs on various sheets. When such sheets arealigned a desired net transparency related to the layering alignment ofthe clear and opaque subregions of the glyphs may be produced.

A glyph may be enhanced (1202). Enhancement of a glyph may includeincreasing the extent of the opaque regions. For example, an overlayglyph which is 50% opaque, and 50% clear or transparent, may beaugmented to have additional opaque area, and/or less clear area. Insome embodiments, enhanced glyphs may be easier to align. In someembodiments, the overlay of enhanced glyphs may have less leakage oflight near subregions where a transparent subregion rendered on onelayer in one glyph is adjacent to a transparent subregion of anotherglyph rendered in another layer. In some embodiments, enhanced glyphsmay produce a greater contrast ratio between overlays having a desirednet transparency of zero, and other overlays which have some intendednet transparency. Examples of enhanced glyphs are discussed inconjunction with FIG. 13.

An enhanced glyph may be used or recorded (1203). For example, anenhanced glyph may be printed in place of the original glyph. As anotherexample, a glyph may be stored for future use, including repeated use.In some embodiments, a collection of glyphs may be processed in thismanner, and the enhanced glyphs may be stored for future use.

FIG. 13 is a diagram showing samples of enhanced contrast overlayglyphs, according to some embodiments. In this example, a 50% blackoverlay glyph 1301 is a square glyph, consisting of 16 sub-regions, 50%(8) of which are opaque, and 50% (8) of which are clear. In someembodiments, an overlay glyph may be used in visual decryption, forexample as described by Naor and Shamir, “Visual Cryptography,”presented at EUROCRYPT '94 and currently available on the internet fromCiteSeer, which is included herein by reference for all purposes. Forexample, by placing and perfectly aligning the 50% overlay glyph 1301 ontop of second copy of that glyph, for example on a second sheet of paperor on top of a display device an opaque region or a 50% transparent,translucent, uncolored or white region may be created, depending onwhether the glyphs are rotated 90 degrees relative to each other or not.

A greater than 50% black glyph 1302 is an example of a glyph with the 8black subregions enlarged, and includes enlargements that extend beyondthe boundary of the overall 4×4 square subregion. Such a glyph may, forexample, enlarge a colored subregion by a fixed amount, such as onepixel around the perimeter of a colored subregion, or 10% of the widthof the colored subregion. Such a glyph may be used to increase thecontrast ratio in an overlay between a resulting opaque region and aresulting less than 50% transparent region. For example, by increasingthe background light behind overlaid glyphs the partially transparentregions visible through identically oriented glyphs may be made brighterrelative to the dark sections created by overlaid pair of glyphs rotated90 degrees relative to one and other.

A greater than 50% black glyph 1303 is a second example of a glyph thatmay be used to enhance the contrast ratio in an overlay of relatedglyphs. In this example, the 16 subregions are framed in black,effectively enlarging the 8 black subregions, as well as framing the 8clear subregions. Such a glyph may, for example, enlarge a subregion bya fixed amount, such as one pixel around the perimeter of a subregion,or 10% of the width of the subregion.

An example of two glyphs similar to the glyph 1302 rendered next to eachother on a single layer is shown in 1312. In this example, each of theglyphs has a 90 degree rotation relative to the other; two of theenlarged black subregions may overlap with subregions of the adjacentglyph; and two of the clear subregions in adjacent glyphs may blend intolarger rectangular clear regions.

An example of two glyphs similar to the glyph in 1303 rendered next toeach other on a single layer is shown in 1313. In this example, each ofthe glyphs has a 90 degree rotation relative to each other; the adjacentblack subregions from each glyph may overlap; and the adjacent framesaround clear subregions in adjacent glyphs may overlap.

FIG. 14 is a flow diagram of a method for using enhanced glyphs,according to some embodiments. In this example, a binary pixel value isreceived (1401). For example, a pixel may have an uncolored or opaquevalue. In this example, a opaque value representation may besignificantly or totally opaque, devoid of light, black, or colored witha tint including for example red, green or blue. In this example, anuncolored value representation may include a region that is at leastpartially white, clear or translucent.

A first enhanced contrast glyph may be selected (1402). An example of anenhanced contrast glyph is discussed in conjunction with FIG. 13. Insome embodiments, an enhanced glyph may have an aggregate colored areathat is larger that the aggregate uncolored area of that glyph. In someembodiments, colored areas may be black. In some embodiments, uncoloredareas may be white. In some embodiments, uncolored areas may betranslucent. In some embodiments, a selection of the first glyph may bemade pseudorandomly from among enhanced glyphs.

In this example, a second enhanced contrast glyph is selected (1402).For example, if the pixel provided has an uncolored value, then a secondglyph that is substantially similar may be selected. As a secondexample, if the pixel provided has a dark or colored value, then a glyphmay be selected which is opaque in some region that was uncolored in thefirst glyph. In some embodiments, a glyph may be selected that is opaquein all regions that the first glyph was uncolored. In some embodiments,the second glyph selected may be a normal contrast glyph.

In this example, the pair of glyphs is used in an overlay (1404). Forexample, the glyphs may be rendered on different layers of a medium insuch a way that they are placed on overlapping regions. For example, oneglyph may be printed on one piece of paper or plastic, and the otherglyph may be printed in an aligned region on a second piece of paper orplastic. In some embodiments, backlighting may be provided so that lighttransmitted through both glyphs, if any, may be observed.

FIG. 15 is a diagram illustrating the result of perfectly alignedoverlaps of two overlay glyphs, according to some embodiments. In thisexample, the top row shows the overlay glyph rendered in a givenposition on a top sheet, the far left column shows the overlay glyphrendered in a the corresponding position on a bottom sheet, and theinternal 4 entries in the table show the resulting image formed by theoverlay composition of the two glyphs. The glyphs used in this exampleare the 50% transparent glyphs such as 1301 of FIG. 13, optionallyrotated by 90 degrees. The center column illustrates overlap resultswhen a bit value of 0 is represented in the top sheet, and the far rightcolumn illustrates overlap results when a bit value of 1 is representedin the top sheet by the same glyph rotated 90 degrees. Similarly, thecenter row and bottom row correspond to bit values of 0 and 1respectively, as represented in the bottom sheet by each of the twoindicated glyphs.

FIG. 16 is a diagram illustrating the result of combinations of alignedoverlays of glyphs, according to some embodiments. In this example, twobits of data represented by XYB, such as 00B, 01B, 10B, or 11B, arerepresented on each of two overlapping layers by a glyph. The glyph usedfor XYB in each layer of this is example is shown in 1601, where X andX′ are rendered as complements of each other (clear vs. black), and X isrendered as clear if and only if the corresponding bit is a 1.

The table 1602 in this example shows in the top row the resulting glyphsused for each of the four possible bit patterns and rendered in a topsheet, while the far left column shows the glyphs that may be renderedfor those 4 patterns on the bottom sheet. The lower right 16 elements ofthe table show the resulting overlay combination of the overlappingglyphs.

FIG. 17 is a diagram illustrating the result of combinations of alignedoverlaps of glyphs, according to some embodiments. In this example, theglyph used for XYB in each layer of this is example is shown in 1701.The table 1702 provides illustration of the results from overlappingrenderings on a top and bottom sheet, as was analogously described inconjunction with 1602 of FIG. 16.

FIG. 18 is a flow diagram of a method for using overlay glyphs to renderan array of data, according to some embodiments. In this example, anarray of data is received (1801). For example, as discussed inconjunction with FIG. 2, an array of data may be received for printingin 241 after assembling 220. In that example, in the context of a vote207 which is an image, the array may consist of two-bit elements, inwhich one bit of each element is an XOR encrypted pixel of that image,and the other bit is a pseudorandomly generated bit.

Each array element may be encoded into an overlay glyph (1802). In someembodiments, a lookup table may be consulted for each element of thearray. In the example of two bits of data per array element discussedabove, a lookup table such as that provided in the top row of FIG. 17may be used to translate values to glyphs.

The array of glyphs may be rendered (1803). In some embodiments,rendering may include printing.

FIG. 19 is a flow diagram of a method for presenting overlays, accordingto some embodiments. In this example, two or more overlays are received(1901). An overlay may be a printed sheet, or a presentation on adisplay device, such as a video monitor or LCD monitor.

The overlays may be aligned (1902). For example, a mechanical device,such a printer, may place and hold the overlays in the desiredalignment. In some embodiments, a user may manually align the overlays.For example, alignment may consist of manually aligning the edges of twoor more printed sheets. As a second example, the alignment may beperformed visually by a user aligning related alignment marks that maybe printed on a sheet. Examples of such alignment marks include marksthat are rendered on the background overlay and/or foreground overlay aswell as physical marks on the background presentation device. In someembodiments, an optical scanner may be used to locate and align thesheets, for example by controlling the position of alignment marks andassociated media, such as paper, electromechanically.

Backlighting of the overlays for viewing (1903) may be provided. Forexample, a light source behind a translucent sheet may provide lightingthat may pass through translucent subregions of glyphs in all layers,and may be obstructed by opaque subregions in any layers. For example,two layers printed in 241 and 243 as discussed in conjunction with FIG.2 may be received, aligned, and backlit.

In some embodiments, the rearmost layer may be a display device thatprovides illumination, such as an LCD display, and backlightingillumination may be provided only in subregions that are defined asclear in that rearmost rendering.

In some embodiments, such as the assembling of bits as discussed inconjunction with 220 and 221 of FIG. 2, pairs of bits in the top layerand bottom layer may be either identical, or complements. For example,if the top sheet is 01B, then the bottom sheet will either be 01B or10B. If glyph representation used a static lookup table, such asprovided in FIG. 17, then the backlit overlay as described inconjunction with 1903 in this example may reveal to a user an image ofthe vote 207 of FIG. 2. In this example, only such top-bottomcombinations (identical or complements) are facilitated, and a resultingcomposition of aligned top and bottom sheet glyphs may produce either a50% brightness (identical glyphs in top and bottom sheet) or 0%brightness (complementary glyphs in top and bottom sheet)

FIG. 20 is a flow diagram of a method for translating an overlay into anarray of data, according to some embodiments. In this example, anoverlay is received. For example, a sheet containing a collection ofoverlay glyphs may be received, such as a sheet printed in 241 anddiscussed in conjunction with FIG. 2.

Individual glyphs may be translated to original data (2002). Forexample, a printed sheet may be scanned, and location of one or moreglyphs on the sheet may be determined relative to an edge of the sheet,or an explicit or implicit alignment mark. An example of an implicitalignment mark is an average or limit of a ragged edge of an encryptedimage. Subregions of an overlay glyph may be determined relative to theposition of a glyph. If the glyph is sufficiently unique, then theprecise data that created the glyph may be determined in this example.For example, when two bit glyphs such as those described in conjunctionwith FIGS. 16 and 17 are used to represent bit pairs, a bit pair may beuniquely recovered from each glyph.

An array of data may be returned (2003). For example, an array of data,with elements corresponding to one or more translated glyphs, may bereturned.

FIG. 21 is a flow diagram of a method for recovering a vote image,according to some embodiments. In this example, an array of data isreceived (2101), in the form of an array of two bit elements. Forexample, the array of data may be voting data recorded in 250 or 252 asdiscussed in conjunction with FIG. 2. As a related example, the arraymay be received by decoding a printed image 241 or 243 as discussed inconjunction with FIG. 2, using decoding techniques discussed inconjunction with FIG. 20.

The encrypted data may be extracted (2102), for example by discardingthe high or low order bit of the two bit quantity in each array element.The retained bit may be the result of XOR 212 or 213 as discussed inFIG. 2.

In this example, the discarded bit may be the direct output of a PRNG211 or 213 as discussed in conjunction with FIG. 2. In some embodiments,otherwise discarded PRNG bits may be used to validate correctness ofPRNG functionality. An example of using discarded PRNG bits to validatecorrectness is to compare an otherwise discarded array with bitsgenerated using an identical seed, such as the seed revealed in 240 or244 and published in 250 or 252 as discussed in conjunction with FIG. 2.

The encrypting PRNG output may be recovered from the escrow (2103). Insome embodiments, the escrow may be obtained from a repository where itwas published in 232 as discussed in conjunction with FIG. 2. The PRNGoutput may be reconstructed from that escrow using techniques discussedin conjunction with FIG. 4.

The data may be decrypted (2104). For example, the encrypting PRNGoutput may be XORed with the encrypted data to recover a vote image. Inthis example, the complete image of the vote is recovered.

In some embodiments, redundancy may be added to vote image data prior toencryption or encoding, for example by replicating the value of one ormore pixels. In some embodiments, every pixel may for example bereplicated into an adjacent row, producing an image that has twice asmany rows. In some embodiments, columnar replication may be used. Insome embodiments, such redundancy may be used to recover an originalvote image when decryption provides only a subset of the encryptedimage. For example, if encryption followed by decryption decimates animage, for example using a “checkerboarding” scheme as proposed by DavidChaum, and produces only a sampling of an image, such as a checkerboardselection of 50% of the pixels, then the replication redundancy prior toencryption may be used to ensure complete recovery of a vote image. Insome embodiments, glyphs corresponding to replicated pixels may haveaspect ratios that compensate, partially or fully, for the replication.For example, if columnar replication is used, then glyphs representingsquare pixels may be used that are approximately twice as high as theyare wide.

FIG. 22 is a flow diagram of a method for incorporating alignment marksinto a rendering of data for overlay, according to some embodiments. Inthis example, an array of data is received (2201). For example, a twodimensional array of data, each entry of which may consist of 2 bits, oreach entry of which may consist of a single bit, may be received. Anexample of such data was discussed in conjunction with assemblies 220and 221 of FIG. 1.

Layout of the array and one or more alignment marks may be determined(2202). In some embodiments, the received array may be numeric, andlayout may include selection of coding glyphs for the items in thearray, such as overlay glyphs. In some embodiments, the array may be arepresentation of a rendered image, such as a bit map. The layout of oneor more alignment marks may include determination of positions for thosemarks, for example placing a pair of alignment marks at opposing cornersof an image.

In some embodiments, alignment marks printed on one or more layers maybe used to facilitate correct alignment of overlay glyphs. For example,when using overlay glyphs, alignment markings can be added to some orall layers to facilitate alignment. The addition may be madeindependently of the media types in each layer (including printed,electronic, etc.). Related alignment marks can be placed on some or alllayers. In one embodiment, alignment marks are related (at a givenoverlapping point on the media) by being identical to those provided inanother layer, and in other embodiments they may be related by beingcomplementary to what is provided on another layer. In some embodiments,several alignment marks can be placed on each layer. For example, atleast two marks can be placed in relatively distant points of a layer ofthe media (for example, close to opposing corners of a rectangularimage), with related or identical marks on the corresponding areas ofsome other. In some embodiments, the alignment marks on one layer may becomposed of one or more images, some or all of which include twocrossing lines. In other embodiments, alignment marks on one layer maybe composed of one or more images, some of which include two or moreparallel lines. The color of portions of the overlapping alignment markimage may optionally be varied from layer to layer. An example of analignment mark is two crossed lines, for example two lines crossed at a90 degree angle, optionally within a circle, and/or optionally missingthe central crossing points of the lines.

Data may be rendered (2203). Rendered data may include the display ofalignment marks and the representation of the array. Rendering mayinclude printing, for example printing 241 and 243 as discussed inconjunction with FIG. 1.

FIG. 23 is a flow diagram of a method for rendering and blurring anoverlay image, according to some embodiments. In this example, anoverlay image is received (2301). In some embodiments, the image may bea dot matrix, including for example the result of encoding data usingoverlay glyphs. In some embodiments, the image may be an array of data,some of which may need to be encoded for rendering using overlay glyphs.

The image may be rendered and blurred (2302). In some embodiments,rendering may include printing. In some embodiments, blurring may beused to enhance readability of images, such as encrypted imagessuperimposed for visual decryption. A blurring may for example beconstructed by physically overlaying an image with a translucentmaterial, such as a sheet of paper or plastic (such as Acrylite GP DP-9)or glass (such as Saint-Gobain Smoothlite), and/or by relocating(exchanging) one or more subregions or pixels of some or all overlayglyphs placed in a specific position in a rendering, with subregions orpixels of some or all overlay glyphs placed in a nearby position in arendering. For example, when an image is rendered using overlay glyphsas part of a visual cryptographic decoding, subregions or pixels thatcompose a glyph may be exchanged (before rendering) with subregions orpixels in an adjacent glyph. In this example, an exchange may beperformed for all glyphs that might be selected to overlay the exchangedregions. In some embodiments, this relocation of subregions may beperformed in all layers of the renderings. As an example, when a glyphis composed of two subregions AB, and is adjacent to a glyph having twosubregions CD, then rather then rendering the adjacent glyphs as ABCD,they can be rendered as ACBD. Blurring may be performed across arendered image, with consistent or pseudo-random variations across theimage, such as varying as a function of the row whether glyphs incolumns 2 and 3 are blurred, or whether columns 1 and 2 as well as 3 and4 are blurred, or all three blurrings are used. In some embodiments,blurring may be performed between subregions in nearby rows and/orbetween nearby columns of glyphs.

FIG. 24 is an illustration of a set of overlay glyphs for use increating a gray level composite image, according to some embodiments. Inthis example, an overlay glyph is defined within a rectangular region,which consists of 16 subregions with reference numbering shown in 2499.When more than one glyph is overlaid in a single region, such as printedon overlapping media, such as translucent or transparent paper, acomposite glyph is formed in this example. The composite glyph mayprovide a gray level of net transparency in the rectangular region. Thegray level may be between 0 (opaque) and the transparency of an overlayglyph. In this example, all glyphs have an individual transparency of50%, and a total of 9 gray levels may result by overlaying variousglyphs.

FIG. 25 is a flow diagram of a method for constructing a set of overlayglyphs for presentation of gray levels, according to some embodiments.In this example, a region is selected (2501). For example, a contiguousrectangular region may be selected. In some embodiments, noncontiguousregions may be selected.

A subregion count S may be determined (2502). In this example, tosupport rendering of G gray levels, S may be selected to be at least2*G−2. For example, to support 9 gray levels, 16 subregions are needed.

The region may be partitioned into S subregions (2503). For example, arectangular region may be divided into a lattice of subregionrectangles. In some embodiments, each subregion may be of substantiallysimilar total geometric area. In some embodiments, each subregion iscontiguous. In some embodiments, some subregions may includenoncontiguous parts.

The subregions may be ordered sequentially (2504). For example, each ofthe S subregions may be identified by an integer from 1 to 5 or 0 to S−1for reference, and those reference numbers may define the sequencing ofthe subregions. For example, 2499 of FIG. 24 provides a sample referencenumbering of 16 subregions within a rectangular region. In someembodiments, a reference numbering may be selected to reduce or minimizecontiguous subregions associated with consecutive numbers.

A total of S distinct glyphs may be specified (2505). A glyph may bespecified to have a first clear subregion at some position in thesequence of subregions, followed by G−2 sequentially identifiedsubregions that are also clear, and the following S-G+1 subregions maybe opaque. In this example, the subregion that sequentially follows thelast subregion is defined to be the first. Using the example referencenumbers for each subregion, the subregion referred to as S is followedsequentially by the subregion with the reference number 1. Each glyphmay be associated with a reference number in a sequence of glyphs in therange of 1 to 5 or 0 to S−1 that is associated with, for example equalto, the first clear subregion in the glyph. In some embodiments, the“first” clear subregion is only considered to be 1 if the subregion S isnot clear, as the “first” clear subregion is followed by G−2 sequentialsubregions that are clear.

For example, the glyph 2400 of FIG. 24 has opaque sequential subregions1-8, and clear sequential subregions 9-16. As a second example, theglyph 2412 of FIG. 24 has opaque sequential subregions 13-16 and 1-4,and clear sequential subregions 5-12.

The lower section 2495 of FIG. 24 provides examples of 16 distinctoverlay glyphs, created as just described. Each of the overlay glyphs,such as 2400 and 2412, has 8 opaque subregions, and 8 clear subregions.

FIG. 26 is a flow diagram of a method for encoding a gray level into twooverlay glyphs, according to some embodiments. In this example, a graylevel d may be received (2601). In this example, a gray level d of 0will produce a maximally transparent net overlay brightness, and alarger positive value of d will produce progressively darker net overlaybrightness. In this example, d is in the range of gray levelsappropriate to the collection overlay glyphs. A set of S glyphsconstructed as described in conjunction with FIG. 25 may be provided,such as the glyphs described in FIG. 24. In some embodiments, thetechnique of FIG. 26 may be repeated for all pixels in an image, byprocessing the gray level of each pixel.

A first glyph may be selected (2602). In some embodiments, a fixedpattern of selection of a first glyph may be used, for example alwaysselecting a specific glyph, or regularly cycling through availableglyphs each time this process is performed. If encryption is beingapplied, then a pseudorandom selection of the first glyph may beperformed in this example. For example, a pseudorandom number may bereduced modulo S−1 to select a glyph from among S possibilities. In someembodiments, a pseudorandom number may be dependent on a private key, orthe position of the encoded pixel in an image that is being encrypted.

A second glyph may be selected (2603). For example, if the glyphs areconstructed as discussed in FIG. 25, with reference numbers asdiscussed, then a second glyph may be selected by adding the gray leveld to the glyph reference number of the first glyph, or by subtractingthe gray level d from the glyph reference number of the first glyph. Forexample, if d is 0, then the second glyph is selected to be identical tothe first glyph in this example. If the second glyph's reference numberis greater than S, then the sum is reduced by S in this example. If thesecond glyph's reference number is less than the minimum referencenumber, then it is increased by S in this example. For example, if thefirst glyph's reference number is S, and the value of d is 1, then S+dis equal to S+1, which is greater than S. In this example, the sum maybe reduced by S, and a glyph with reference number (S+1)−S, or 1, may beselected.

The pair of selected glyphs may be provided (2604). Provided glyphs maybe used for rendering, for example placing a first glyph on a top layerand the second glyph on a lower layer, so that they may be aligned andviewed. The properly aligned physical overlay of any two such overlayglyphs, for example constructed as discussed in FIG. 25, results in acontinuous sequential series of opaque subregions. When two glyphs areoverlaid, their net (overlay) darkness varies proportionately to thedistance between the start of each glyphs sequentially darkenedsubregions. For example, the overlay of glyphs 2400 and 2412 is shown as2490 in FIG. 24, and includes opaque subregions 13, 14, 15, 16, 1, 2, 3,4, 5, 6, 7, and 8, for a total 12 opaque pixels, and 4 clear pixels, andhence a 75% transparency.

In some embodiments, a pair of returned glyphs as discussed inconjunction with 2604 may be published and presented in any way thatpermits visual overlay. Examples include printing on paper or atransparent or translucent medium, or displaying one layer on a displaydevice such as a CRT and providing a printed overlay of another layer,displaying two layers on two electronic display devices that can beoverlaid, such as transparent LCD panels, and algorithmically combiningtwo images received electronically and combining them on a singledisplay device such as a CRT.

In some embodiments, a glyph set used to represent a gray level in onelocation in an image may be different from a glyph set used in anotherlocation in an image. For example, the region and shape encompassed mayvary between glyph sets. In some embodiments, overlay glyphs that canrender 128 distinct gray levels may be specified using 254 subregionsper glyph. In some embodiments of such glyphs, the first (for example,top left) glyph region may consist of 16×16 subregions, minus twosubregions (for example, at the bottom right), for a total of 254subregions. The next glyph region (for example, immediately to the rightof the first glyph) could consist of 16×16 subregions, plus the twosubregions from the first glyph, minus 4 subregions from the right handside of the 16×16 region. This pattern could continue, in which a 16×16glyph is usually augmented by the excess subregions on the previousglyph (to the left), and excess subregions in that new glyph are usuallycontributed to the next glyph's footprint (to its right). After a totalof 8 such glyphs, the augmentation can amount to a full column ofsubregions, and the center of the next 16×16 glyph can be establishedone subregion's width to the left of its canonical position. Thisprocess is an example of the use of non-square glyph regions, and isalso an example of the use of different glyph sets for differentregions, as well as the use of a rectangular array of subregions insidea non-rectangular glyph region.

As a second example of the above 128 gray level glyph definitions, a16×16 area of subregions can again be used as the basis of each glyph,but the excess subregions can be contributed to distinct adjacentglyphs. For example, since each glyph consists of 254 subregions, theexcess subregions (in an otherwise square 16×16 area) can be contributedso that one extra goes to the next glyph to the right, and the otherextra goes to the next glyph to the bottom. After 16 such columns ofglyphs, the accumulated excess subregions can total a full edge of thenext 16×16 glyph, and its effective center can be shifted onesubregion's width to the left. Similarly, after approximately 16 rows ofsubregions, the accumulated subregions can cause the next row of glyphsto be centered one subregion's height higher.

Using the above approach (contributing some extra subregions to theright, and some downward), nearly square collections of subregions canbe used to represent square glyph areas. As another example, an 8×8(square) glyph region, with glyphs having 254 subregions, can be placedin an almost square 128×127 subregion rectangle. As another example, asquare 2544×2544 region, with glyphs occupying each region having 254subregions each, can be placed in a 557568×557567 subregion rectangle.As another example, a 60×60 region, with glyphs having 14 subregions(potentially providing 8 gray scale levels), can fit exactly into a225×224 subregion rectangle. As another example, a 1798×1798 region,with glyphs having 14 subregions, can fit exactly into a 6728×6727subregion rectangle. As another example, a 6×6 region, with glyphshaving 510 subregions (potentially providing 256 grayscale levels) canperfectly fit in an almost square 136×135 subregion rectangle. Asanother example, a 1544×1544 region, with glyphs having 510 subregions,can perfectly fit in an almost square 557184×557183 subregion rectangle.

FIG. 27 is a flow diagram of a method for establishing authenticationcredentials, according to some embodiments. In this example, a userauthenticates an identity to a registrar (2701). In some embodiments, auser may be an eligible voter, a registrar may be a government officialempowered to perform voter registration, and the authentication mayinclude presentation of a proof of identity such as a driver's license,and proof of residency.

An authentication token may be constructed (2702). Examples of anauthentication token include a shared secret, such as a password orpassphrase, and a physical device, such as an electromechanical devicethat contains or can process a private cryptographic key for use inauthentication. A shared secret may be constructed by the user, or theregistrar, or an assisting device, or a combination of one or more ofthe above.

A record may be made of the distribution of the authentication token(2703). For example, if the authentication token is a passphrase, arecord of the passphrase may be recorded by the registrar. As anotherexample, if an authentication token is a physical device, then a recordmay be made of details of that device(s), such as recording a public keyassociated with the device, or a serial number associated with thedevice. An example of a physical device includes a set of one or moreRFID tags. In some embodiments, more than one authentication token maybe provided, for example one valid authentication token and one or moreinvalid authentication tokens.

The authentication token may be used by the user as an authenticationcredential, for example as discussed in conjunction with FIG. 28.

FIG. 28 is a flow diagram of a method for creating a partiallyanonymized message, according to some embodiments. In this example, auser creates a message (2801). In some embodiments, a message may be avote, such as a vote to be transmitted as part of an absentee ballot. Avote may for example be in the form of a printed ballot that is markedwith preferences by hand, or may be a printed ballot created by a user'scomputer, or may be a vote contained in digital media, such as solidstate or magnetic media.

In some embodiments, when a message such as a vote is constructed, auser may use trusted software delivered via a trusted channel. Anexample of trusted software distribution is discussed in conjunctionwith FIG. 30, and an example of executing trusted software is discussedin conjunction with FIG. 31. For example, media such as a CDROM may beacquired from a trusted source such as a governmental agency. Such mediamay contain trusted application software and/or a trusted copy of anoperating system. For example, a bootable CDROM may be used thatcontains Microsoft Windows 98 or Mac OS X along with ballot generationsoftware. Ballot generation software may for example include votingoptions appropriate to a voter such as candidate names and line itemsapplicable to the voter's voting district, and public keys needed forencryption or authentication. In some embodiments, such ballotingsoftware may create a printed ballot, or a file representing a ballot.In some embodiments, some additional steps described below may beperformed by such balloting software.

The message may be enshrouded (2802). For example, a paper message maybe placed into a sealed envelope to enshroud the contents. An electronicrepresentation of a vote may be enshrouded by means of encryption, forexample by encrypting with a public half of a public/private key pair,or by visually encrypting using an escrowing PRNG as described inconjunction with FIG. 3. An encrypted message, such as a vote, mayoptionally be printed using methods such as are discussed in conjunctionwith FIG. 2.

In some embodiments, a second computer may be used to validate theproduction of a message. For example, if a message is enshrouded usingvisual encryption, a second computer, such as a second home computer,may independently generate a decryption mask.

A receipt may be added (2803). In the case of a sealed envelope, anexample of a receipt is a hand-written phrase on the outside of theenvelope. In some embodiments, a recipient may allow a sender to reviewa list of received message receipts, including receipts associated withmessages sent by a given sender. In an electronic form, a receipt mayinclude the addition of more data, or the embedding of receipt data intoan existing enshrouded message. An example of embedding receipt datainto an existing enshrouded message is to include an area in a messagefor receipt data, for example an area that is all zero bits, or an areathat is prepopulated with receipt information. A receipt may be added byXORing a receipt into an enshrouded message in an area designated forreceipt data.

A message with a receipt may be enshrouded (2804). For example, a paperenvelope provided earlier may be enclosed in a new outer envelope. Asanother example, enshrouding of an electronic message may be performedby encrypting, for example by encrypting with a public half of apublic/private key pair.

An identifier specifying the sender may be added (2805). For example, inpaper based embodiments, the name of the user may be signed, written orprinted on an envelope. In an electronic embodiment, a user maycryptographically sign the data.

A message with an ID may be enshrouded (2806). For example, in a paperbased embodiment, an envelope may be used to surround prior envelope(s)or message. As another example, in an electronic embodiment, the datamay be encrypted.

Authentication may be added (2807). Authentication credentials may bebased on an authentication token, such as discussed in conjunction withFIG. 27. For example, in a paper based embodiment, where anauthentication token of the form of a shared secret has been provided, acopy of that shared secret may be affixed to the current set ofenclosing envelopes, if any, or to the message. If for example theauthentication token is an electromechanical device, then that devicemay produce a message or secret for use in this authentication, such asa word or phrase. If for example the authentication token includes oneor more RFID tags, then such a tag may be affixed.

A message with an authentication may be enshrouded (2808). For example,in a paper based embodiment, an enclosing envelope may be applied.

The fully enshrouded message may be transmitted (2809). For example, ina paper based embodiment, an outer envelope may be addressed and send bymail to a receiving party. In an electronic environment, a digitallyenshrouded message may be transmitted via a network such as theinternet, or the digitally enshrouded message may be recorded on digitalmedia such as magnetic, optical or solid state media and physicallytransmitted to the recipient.

FIG. 29 is a flow diagram of a method for processing a partiallyanonymized message, according to some embodiments. In this example, amessage is received that may be enshrouded (2901). For example, amessage constructed and enshrouded as discussed in conjunction with FIG.28 may be received. Examples of reception include arrival of anenvelope, such as via the US Postal Service, receipt of digitalinformation over a network such as the internet, and receipt of digitalmedia such as magnetic, optical or solid state media containing amessage. In some embodiments, a message may include a ballot.

An outer shroud may be removed (2902). For example, an outer envelopemay be removed, or data may be decrypted to some extent, for exampleusing the private half of a public/private key pair.

An exposed authentication token may optionally be validated (2903). Forexample, a shared secret may be readable, and may be checked against alist of valid authentication credentials. Examples of valid credentialsinclude authentication tokens distributed by a process such as wasdiscussed in conjunction with FIG. 27.

If an exposed authentication credential is not determined to be valid(2904), then the remaining (possibly enshrouded) message is discarded inthis example (2905). If an exposed authentication credential isdetermined to be valid, then related authentication information isprocessed in this example (2906). An example of related informationincludes the name of the user that was authorized to use theauthentication credential. A second example of related information mayinclude information such as a passphrase that may be cross-checkedagainst user identity information if and when such identity informationis revealed. In some embodiments, absence of an authenticationcredential may be interpreted as valid, and there may be relatedinformation associated with such an absence, such as a statement that noauthentication credential was supplied. In some embodiments, anidentifier associated with the message may be associated withauthentication information, for example authentication information thatmay be cross-checked with identity information, and transmitted to anauthentication entity. In some such embodiments, authenticationinformation may be discarded after transmittal to an authenticationentity.

Processing of authentication (2906) may include adding some relatedinformation to the remaining message data, and such data that may beused in concert with other potentially enshrouded information, forexample by cross checking. For example, in a paper based scenario, datafor later cross-checking when another enclosing envelope is opened maybe affixed to that envelope. In an electronic shrouding example thatmakes use of encryption, data for later cross checking may be insertedinto the shrouded message, such as by appending it (with optionalappropriate encryption), or by XORing into a predetermined section of ashrouded message.

In some embodiments, processing of an authentication (2906) may includerecording that a credential has been used. In some embodiments, thenumber of uses of a credential may be limited, for example limited toone use. In such embodiments, use beyond a threshold may be determinedto be invalid.

A shroud around identification information may be removed (2907). Forexample, in a paper based embodiment an enclosing envelope may beremoved, or in an encryption based embodiment another layer may bedecrypted, for example using the private half of a public/private keypair.

An exposed identification may be validated (2908). Validation mayinclude checking against a list of authorized users. Validation mayinclude checking the validity of an identifying signature, for examplevalidation of a cryptographic signature, or validation of a writtensignature against a prior facsimile.

Validation of identification may include cross checking informationrelated to authentication. In some embodiments, validation may includeassociating identification information with an identifier associatedwith the message and transmitting it to an authentication entity. Anauthentication entity may check the identification information againstauthentication information such as a passphrase that is associated withthe identifier, and determine whether the authentication information isvalidly associated with the identification information. In someembodiments, in which related authentication information was XORed intothe enshrouded (encrypted) message, validation may include verificationthat a portion of the message is a predetermined pattern, for examplebecause the authentication related information canceled out informationprovided in a portion of the plaintext identification. Examples of apredetermined pattern include a blank area, an area with a regularpattern, and an area which includes data conforming to a codingstandard. One example of a coding standard is arbitrary data plus anerror detecting code, such as a parity or checksum for the random data.In some embodiments, validation may include determining that a portionof the message is well-formed, for example that it containsappropriately formatted data. In some embodiments, cross checking mayinclude an affirmative comparison between some data associated with theidentification, and the data that was related to the authenticationcredentials. An example of can affirmative comparison is validating thattwo pieces of related information are similar.

In some embodiments, validation of the identification may includetesting to see if the identification has been used more often than athreshold number of times, such as used more than once. For example, ina voting application, validation may include recording that anidentified user has voted, and determining that the identification isinvalid if more than one voting message has been received from anidentified user.

If the identification is not determined to be valid (2909), then theremaining message is discarded in this example (2910). If theidentification is determined to be valid, then related information isprocessed in this example (2911). Related information may include theidentity of the user, information related to the identity such asinformation in an external list associated with the identity,information related to the authentication credential, informationconstructed as a function of one or more of the previous items, such asvia a cryptographic hash.

Processing of identification related information (2911) may includeadding some related information to the remaining message data, and suchdata may be used in concert with other potentially enshroudedinformation, for example by cross checking.

A shroud around receipt information may be removed (2912). For example,in a paper based embodiments an enclosing envelope may be removed, or indigital embodiments another layer may be decrypted, for example usingthe private half of a public/private key pair.

Receipt information may be validated (2913). In some embodiments, allreceipt information may be considered valid. In some embodiments, onlyreceipt data of a given format or size may be considered valid. In someembodiments, the absence of receipt data, such as no data or a nullstring, may be considered valid.

If the receipt data is determined to be valid (2914), then informationrelated to the receipt data may be processed in this example (2915).Information relating to the receipt data may include the receipt data,information related to identification, information relating toauthentication, or a calculated combination of one or more items, forexample calculated via a cryptographic hash function or encryptionfunction. Processing may include recording or publishing suchinformation. For example, recorded receipt related information may bemade available to a user that constructed a message. Processing mayinclude adding some information to a remaining (possibly shrouded)message, and such data may be used in the processing of the possiblyenshrouded message.

In this example, if the receipt data was invalid, or after the receiptis processed, a shroud (if any) is removed from the message (2916). Forexample, in a paper based embodiment, a containing envelope may beremoved, or in a cryptographic embodiment, a message may be decrypted,for example using the private half of a public/private key pair, or byreconstructing an image using visual cryptography and a data regeneratedfrom an escrow.

A message may be processed (2917). For example, in a voting scenario,processing may include submitting a (vote) message for inclusion in atally. In some embodiments, elements of the message may include data,such as related information added to the message in the above process.Such additional data may become part of the message and includedirectives for handling the message, for example an assertion that theremainder of the message should be discarded, or an assertion that themessage is valid.

An example of the techniques exemplified in FIGS. 27, 28 and 29 appliedto paper-based absentee voting is for a voter to supply identificationto a registrar of voters (4401) and specify a passphrase (2702). Theregistrar associates the passphrase with the voter's identity (2703).The voter fills out an absentee ballot (2801) and includes his or heridentity (2805) and the passphrase on the ballot or an enclosingenvelope (2807). The voter sends the ballot to an election agency(2809). The election agency retrieves the passphrase (2906) andidentification (2908). If the passphrase is determined to match thepassphrase on record for the voter and the voter is determined not tohave previously submitted an authenticated ballot (2909), then theballot is counted in this example (2917). If the passphrase isdetermined not to match the passphrase on record for the voter or if thevoter is determined to have previously submitted an authenticated ballot(2909), then the ballot is discarded in this example (2910).

FIG. 30 is a flow diagram of a method for distributing trusted software,according to some embodiments. In this example, a trusted application isconstructed (3001). For example, an application may be built that allowsa voter to enter votes, encrypt those votes, and records an encryptedrepresentation of the voter's intent, for example by printing, byrecording the intentions in a file, or by transmitting the intentionsvia a network. Another example of a trusted application is anapplication that may be used to validate signatures, including digitalsignatures and hashes including cryptographic hashes. For example, suchan application may produce a checksum when directed at a file, and thatchecksum may be validated against a checksum received via a trustedchannel. As another example of the use of such a validation application,it may be used to validate trusted software, such as a bootable trustedapplication.

A bootable operating system may be obtained (3002). For example, a copyof Microsoft Windows 98, that can fit on a CDROM, and can be used toboot an IBM PC compatible computer, may be obtained. As another example,a copy of Linux that can fit on a CDROM and can be used to boot apersonal computer may be obtained. As a third example, a copy ofMicrosoft DOS 6.0 that can fit on a floppy disk and can be used to bootan IBM PC compatible computer may be obtained. In some embodiments, morethan one bootable operating system may be obtained, such as MAC OS-X andWindows 98. In such examples, both operating systems may be supplied,and the operating system appropriate to the eventual host processor maybe automatically selected, for example selected by the BIOS of the hostcomputer.

A bootable application may be constructed (3003). For example, filesthat direct an operating system to run an application during or aftercompletion of a boot sequence may be constructed to direct the runningof the trusted application. For example, in Microsoft DOS 6.0, a fileAUTOEXEC.BAT may be placed in a root directory containing the name andpath of the trusted application, and that application will be runautomatically when the operating system completes it boot sequence. Insome embodiments, an image may be created, for example an image ofblocks of a bootable CD-ROM or floppy disk. The image may include one ormore bootable operating systems and trusted applications. In someembodiments, information specific to an intended recipient such as avoter may be included in an image, for example by constructing an imageincluding recipient-specific information or by insertingrecipient-specific information into an image. Examples ofrecipient-specific information include identity information,authentication information, and local voting options.

The bootable application may be distributed via a secure channel (3005).For example, the bootable application may be placed on media, such as aCDROM or floppy disk, and that media may be distributed by a securephysical channel. One example of placing a bootable application on mediais writing an operating system and bootable application onto media.Another example of placing a bootable application on media is writing animage onto the media, or stamping media with a preconstructed templaterepresenting an image. An example of a secure physical channel is handdelivery by trusted agents. Another example of a secure physical channelis distribution by a trusted commercial agent, such as a store. Anotherexample of a secure physical channel is distribution by trustedpolitical group, such as a political party. Another example of a securechannel is a channel in which interference is punishable by law, such asthe United States Postal Service. Another example of distribution by atrusted channel is electronic distribution that is validated by atrusted application after receipt by a user. An example of electronicdistribution is distribution via a network, such as the Internet.

FIG. 31 is a flow diagram of a method for executing trusted software,according to some embodiments. In this example, a bootable applicationis received (3101). In some embodiments, a bootable application may bereceived on removable media, such as a CDROM or a floppy disk. In someembodiments, a bootable application may have been created as discussedin conjunction with FIG. 30.

In some embodiments, the bootable application may be received via atrusted channel. An example of a trusted delivery channel is handdelivery, for example by a trusted party, or a police enforced trustedchannel, such as the US Postal Service.

In this example, trusted hardware may be initialized by the receivedsoftware (3102). An example of trusted hardware is a personal computerowned by a user. Examples of initializing trusted hardware turning thecomputer off and on, selecting “restart” from a Windows menu, and anyother way to place the computer in a standard initial configuration. Thebootable application may be read into a memory associated with thetrusted hardware. Reading the bootable application may include loadingmedia, such as a CDROM containing the bootable application; optionallyconfiguring the trusted hardware to boot the media, for example byconfiguring the ROM BIOS; and allowing the computer to run software fromthe CDROM during its bootstrap operation, for example under control ofthe ROM BIOS in the trusted computer. In some embodiments, booting mayinclude running an operating system provided with the bootableapplication.

In this example, the trusted application is executed (3103). In someembodiments, the trusted application may be automatically executed. Forexample, a booted operating system may be preconfigured to execute anapplication provided. An example of such a configuration with aMicrosoft DOS operating system includes the placement of the path andname of an application in the AUTOEXEC.BAT file on the bootable disk.

In some embodiments, the trusted application may be a votingapplication. For example, it may be an application that requests voterinput, and constructs a complete ballot for submission. Examples of suchapplications are discussed in conjunction with foregoing Figures.

In some embodiments, options appropriate to an election may beautomatically provided with the bootable voting application. Forexample, a list of candidates in a district, and propositions for agiven election, may be preconfigured in the voting application.

In some embodiments, a trusted voting application may electronicallysubmit a voter's intent. For example, a user's vote may be transmittedvia a network, such as the internet, or using a removable electronicstorage device, such as a floppy disk or compact flash memory. In someembodiments, transmissions may use cryptographic methods to protect theintegrity and privacy of the voter's intent. For example, electronicsubmissions may use SSL or S/MIME.

In some embodiments, a trusted application may produce a printablerepresentation of a voter's intent. For example, the application mayprint the voter's intent, such as in a completed ballot, optionallyencrypted and/or authenticated. In some embodiments, the printablerepresentation may be stored on a persistent storage device, such as adisk, including the trusted computer's hard disk or removable storagesuch as a floppy disk, flash memory or a memory in a smart card. In someembodiments, a printed vote may be submitted, for example transmitted bymail, or hand delivered to a polling place.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

1. A method for privacy, comprising: providing a pixel value;determining whether the pixel value is associated with coloration;selecting a first glyph; wherein a first aggregate opaque areaassociated with the first glyph is larger than a second aggregateuncolored area associated with the first glyph; and selecting a secondglyph; wherein the first glyph is opaque in a first region correspondingto a second region that is uncolored in the second glyph, if it isdetermined that the pixel value is associated with coloration.
 2. Themethod of claim 1, wherein coloration is associated with black.
 3. Themethod of claim 1, wherein lack of coloration is associated with white.4. The method of claim 1, wherein the first opaque area is associatedwith black.
 5. The method of claim 1, wherein the first uncolored areais associated with white.
 6. The method of claim 1, wherein the firstuncolored area is associated with translucency.
 7. The method of claim1, wherein the first region is contained within a third region, whereinthe third region is opaque.
 8. The method of claim 1, further comprisingsuperimposing the first glyph and the second glyph.
 9. The method ofclaim 8, further comprising illuminating the superimposed first andsecond glyphs from behind.
 10. A method for privacy, comprising:providing a first printed layer and a second printed layer; wherein thefirst printed layer and the second printer layer are associated withvisual encryption; superimposing the second printed layer on the firstprinted layer; and blurring a layer.
 11. The method of claim 10, whereinblurring the layer includes superimposing a diffusive layer on thesuperimposed first and second layers.
 12. The method of claim 11,wherein the diffusive layer is associated with glass.
 13. The method ofclaim 11, wherein the diffusive layer is associated with plastic. 14.The method of claim 10, wherein blurring the layer includes exchanging afirst region and a second region of the layer.
 15. A method for privacy,comprising: providing a pixel value; selecting a first glyph; andselecting a second glyph; wherein the second glyph is separated from thefirst glyph in a predetermined sequence of glyphs by a factor, whereinthe factor is associated with the pixel value.
 16. The method of claim15, wherein the pixel value is one of G predetermined values and whereinthe first glyph includes R predetermined subregions, wherein R is atleast two times G minus two.
 17. The method of claim 15, wherein thefirst glyph is selected randomly.
 18. The method of claim 15, whereinthe first glyph is associated with an index J and wherein determiningthe second glyph includes calculating an index K, wherein K isassociated with J and the pixel value, and wherein selecting the secondglyph includes calculating the remainder of K divided by N, wherein N isthe number of distinct glyphs in the predetermined sequence of glyphs,and selecting the Kth glyph in the predetermined sequence of glyphs. 19.The method of claim 18, wherein calculating K includes selecting a valueof K that differs from J by the pixel value.
 20. The method of claim 15,wherein the predetermined sequence of glyphs contains at least threeglyphs, and wherein for each glyph in the predetermined sequence ofglyphs, all opaque regions of the glyph are consecutive in apredetermined sequence of regions, wherein the first consecutive opaqueregion is associated with the index of the glyph in the predeterminedsequence of glyphs, and wherein the last region in the predeterminedsequence of regions is consecutive with the first region in thepredetermined sequence of regions.